(VB) Extension Method Not Working As Expected?

I have the following Extension Method

Imports System.Runtime.CompilerServices
Namespace Extensions
Public Module IntegerExtensions
<Extension()>
Public Function ToCommaDeliminatedNumber(ByVal int As Integer) As String
Dim _input As String = int.ToString
Select Case int
Case Is > 99999 : Return _input.Remove(_input.Length - 3) & "k"
Case Is > 9999 : Return Math.Round(Double.Parse(int / 1000), 1).ToString & "k"
Case Is > 999 : Return String.Format("{0:N0}", int)
Case Else : Return _input
End Select
End Function
End Module
End Namespace

And in one of my classes I'm using user.Reputation.ToCommaDeliminatedNumber I am importing the Extensions Namespace into the Class, but the error I'm getting is...'ToCommaDeliminatedNumber' is not a member of 'Integer?'. I do have other Extension Methods for Strings and Dates that work exactly as expected... I'm just at a loss on this one.